Abstract
In orthogonal frequency division multiplexing with index modulation (OFDM-IM), the active subcarriers can convey information bits by modulated symbols as well as their indices. OFDM-IM has attracted a great deal of attention from researchers by virtue of high energy efficiency. Unfortunately, OFDM-IM has inherited large peak-to-average power ratio (PAPR) of the classical OFDM signal, but there are few works dealing with it. Selected mapping (SLM) is a promising PAPR reduction technique that is distortionless, has good PAPR reducing capability, and can be easily adapted in OFDM-IM systems. In SLM for OFDM-IM systems, the phase sequences rotate the OFDM-IM block in the frequency domain before the inverse fast Fourier transform (IFFT) is applied. Also, permutation in the frequency domain can be easily introduced before multiplication of phase sequences in SLM. In this paper, we investigate the phase sequence set (PSS) and permutation functions in the SLM scheme for OFDM-IM systems; First, the efficiency of the permutation is analyzed as a function of the number of active subcarriers. Second, the optimal conditions for the PSS and permutation functions are derived, which is verified through simulations.
Highlights
Index modulation (IM) is an emerging technique that exploits indices of active resources to convey information in addition to conventional M -ary modulation symbols
The following simulation parameters are used in all plots; N = 64, M = 4 (quadrature phase shift keying (QPSK) is used), n = 16, and G = 4, which is reasonable because the orthogonal frequency division multiplexing (OFDM) with index modulation (OFDM-IM) system has an advantage over the classical OFDM when they operate at low bit rates [3]
OFDM-IM has become a promising technique whereby the specific activation of the frequency domain subcarriers is used for implicitly conveying extra information
Summary
Index modulation (IM) is an emerging technique that exploits indices of active resources (such as spatial, time, and frequency resources) to convey information in addition to conventional M -ary modulation symbols. In [21], permutation procedure in the frequency domain has been proposed in the SLM scheme for OFDM-IM systems in order to make the subcarrier activation pattern (SAP) in the frequency domain diverse This is because the envelope distribution of the OFDM-IM signal in the time domain depends on the SAP [22]. THE SLM SCHEME WITH PERMUTATION FOR OFDM-IM SYSTEMS Note that the SAP of an OFDM-IM block affects the envelope distribution of the corresponding OFDM-IM signal in the time domain and its PAPR [22]. A. EFFICIENCY OF PERMUTATION IN THE SLM SCHEME FOR OFDM-IM SYSTEMS we investigate whether the permutation procedure in the SLM scheme in Fig. 3 helps to improve the PAPR reduction performance or not. Note that the difference between the left-hand side (LHS) term and the right-hand side (RHS) term in (6) becomes large if the random variable F(I, γ ) has large fluctuation, which leads to the benefit of permutation in the SLM scheme
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